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Could Some Gut Bacteria Cause Colon Cancer?

Colon cancer and the gut microbiome

The gut microbiome can play a role in diseases like irritable bowel disease and obesity and may also play a role in the development of colorectal cancer.

New research has shown that certain types of bacteria may contribute to colon cancer, but doctors and researchers still don’t have clear answers.

If you’re concerned about colon cancer, talk with your doctor about getting screened.

You are never alone: There are 100 trillion little friends living in your intestines, not to mention your stomach and the rest of your body. These friends are bacteria that make up the body’s microbiome. And while most of these bacteria are helpful and help keep us healthy, sometimes something goes wrong.

The gut microbiome has been implicated in the development of many diseases, from irritable bowel disease to obesity. Now, researchers are wondering if it could play a role in whether or not someone develops colorectal cancer.

There were an estimated 135,430 new cases of colon cancer in the U.S. in 2017. It is the third most diagnosed form of cancer and second leading cause of cancer-related deaths. Historically, colon cancer was more common in people over age 50, but doctors have recently been seeing more cases in millennials and Gen Xers.

“The microbiome is uncharted territory, and it’s such a new field of research. I don’t think we can attribute all colon cancer to the microbiome, but the microbiome is critical to understanding disease,” says William DePaolo, Ph.D., a gastroenterologist and director of the Center for Microbiome Sciences & Therapeutics at UW Medicine. “Currently, there are more questions than answers.”

What is bacteria’s role in colon cancer?

Researchers haven’t yet determined if bacteria can cause colon cancer or if it’s to blame for the rise of colon cancer in young people. But new studies have shown that three types of bacteria—Fusobacterium nucleatum, Bacteroides fragilis and a strain of E. coli—may be linked with colon cancer.

All of these bacteria exist in the colon normally and generally aren’t harmful there, says DePaolo.

The problem seems to occur when the bacteria change or expand, releasing toxins into the body that cause inflammation and damage DNA in the colon. They may combine forces and contribute to tumor growth.

Another type of bacteria, F. nucleatum, was found to be prevalent in many colon tumors. When mice were treated with an antibiotic that suppresses this bacteria, tumor growth also slowed.

What about polyps?

Most of the time, colon cancer originates from a polyp in the colon or rectum. Polyps are small growths that form on the colon or rectum’s lining. People can develop polyps without developing cancer, and most polyps aren’t cancerous.

DePaolo and his team are conducting a study to better understand how bacteria may interact with polyps and potentially lead to colon cancer. By taking microbiome samples from pre-cancerous colon polyps, they can determine which bacteria are associated with polyps, and by following patients over time they will find out which of those polyps then become cancerous.

They will also take samples from people who don’t have polyps to see which bacteria populate their colons.

“We’re seeing that there may be no differences in the types of bacteria there are—people with or without colon cancer could have the same types of bacteria," says DePaolo. "We’re more interested in looking on the genetic and metabolic level of these bacteria, to see if they act differently at different sites in the body, and if that could contribute to cancer."

Barring a major disruptive event, gut microbiome bacteria are resilient and don’t change dramatically. Still, DePaolo believes more research should be conducted looking at past widespread events—such as flu outbreaks and food recalls—to see if there is any connection to the sudden outbreak of colon cancer in younger people.

What can you do to keep your gut healthy?

Since researchers don’t know how much the gut microbiome influences colon cancer risk, there aren’t any recommendations yet for how to prevent colon cancer other than getting recommended screening tests. However, if you’re concerned and want to keep your gut healthy, DePaolo has some suggestions.

Make friends, not foes

First, recognize that most of the bacteria in your gut are your friends, though some are not. Problems arise when something messes with your body’s good-to-bad ratio. Stress, lack of sleep and poor eating habits can allow the few bad gut bacteria to grow and multiply and cause things like inflammation or gastrointestinal distress.

Feed the good bacteria

Filling your plate with fruit and veggies and choosing lean meats will help make the good bacteria in your gut happy. Avoid high-fat foods, since fat is easily stored by bad bacteria.

Eat more fiber

Upping your fiber intake is also helpful, since fiber feeds good bacteria and helps prevent inflammation. Many people don’t get enough fiber and don’t realize it. Fruits, vegetables, whole grains and beans and legumes all tend to be high in fiber.

Try fermented foods, starchy foods or cellulose

Eating fermented foods and foods that contain starch or cellulose can also help replenish good bacteria in your gut. Healthy starchy foods include vegetables like peas, corn and potatoes, and grains like rice. Cellulose is prominent in many leafy green vegetables such as broccoli, cabbage and kale.

Be smart about probiotics

Probiotics can be helpful, but do your research before buying. Make sure the product has different species of bacteria, not just one. Species such as Lactobacillus, Bifidobacterium, and Saccharomyces have been shown to be helpful for people who have gastrointestinal problems like diarrhea or irritable bowel syndrome. Some products claim to have more probiotics than they actually do, so check the label. Products with 10 million CFUs (colony-forming units) per species are best.